To enable a talker to hear some of her own voice during a telephone call conversation, telephone handsets implement a sidetone function that feeds back some of the talkers voice to the receiver of the handset. Doing so gives the talker a better feel for the conversation as he can respond to hearing his own voice by adjusting how loudly he speaks, which also benefits the listener at the other end of the conversation. In some telephony handsets, the sidetone level can be manually adjusted by the talker. For example, if the talker is in a noisy environment, such as a windy day or near a railroad track or airport, he can lower the sidetone level, which may help him better hear the other side of the conversation.
Consumers are welcoming the use of in-ear earphones (or simply earbuds) for listening to music that is being played by their portable multifunction devices such as the IPOD and IPHONE handheld devices by Apple Inc. Earbuds facilitate listening to high fidelity sound by making an airtight seal with the users ear canal, behind the earbud's sound output port. The IPHONE device is a multi-function handheld device that can also be used as a cellular telephone handset, i.e. it has “mobile phone” or telephony functionality. Users of such devices may also want to make and answer wireless telephone calls while wearing the earbuds. Therefore, the multi-function device also needs to provide the proper sidetone level through its earbuds, when it is being used as a telephone handset.